Synthesis, characterization, and OLED application of oligo(p-phenylene ethynylene)s with polyhedral oligomeric silsesquioxanes (POSS) as pendant groups

Article abstract of DOI:10.1016/j.tet.2010.10.009

Two new classes of mono- and oligo(p-phenylene ethynylene)s grafted with polyhedral oligomeric silsesquioxanes (POSS) were synthesized via 'click' chemistry and palladium-catalyzed Sonogashira cross-coupling. These materials with cubic silsesquioxanes are very robust with excellent thermal stability in air (T_5%loss>330 °C) and exhibited T_g>80 °C. All the compounds showed high photoluminescence with a range of blue emission and quantum yield up to 80% in the solution. Extended π conjugation molecules of oligo-pPEs POSS maintain relatively high PL quantum efficiencies in the solid state, compared to mono-pPEs POSS. A preliminary report is made of some of the materials as multilayer OLED components with active dopants PVK and PBD.

Full text of DOI:10.1016/j.tet.2010.10.009

Tetrahedron 66 (2010) 9348e9355
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis, characterization, and OLED application of oligo(p-phenylene
ethynylene)s with polyhedral oligomeric silsesquioxanes (POSS) as pendant
groups
,
b
,
a
a
a
a
Vuthichai Ervithayasuporn a , Junichi Abe , Xin Wang , Toshinori Matsushima , Hideyuki Murata ,
*
Yusuke Kawakami a
a School of Materials Science, Japan Advanced Institute of Science and Technology (JAIST), 1-1 Asahidai, Nomi, Ishikawa 923-1292, Japan
b Department of Chemistry, Faculty of Science, Mahidol University, Rama VI Rd., Ratchathewi, Bangkok 10400, Thailand
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 9 July 2010
Received in revised form 7 September 2010
Accepted 4 October 2010
Available online 20 October 2010
Two new classes of mono- and oligo(p-phenylene ethynylene)s grafted with polyhedral oligomeric sil-
sesquioxanes (POSS) were synthesized via ‘click’ chemistry and palladium-catalyzed Sonogashira cross-
coupling. These materials with cubic silsesquioxanes are very robust with excellent thermal stability in
air (T5%loss>330 ꢀC) and exhibited Tg>80 ꢀC. All the compounds showed high photoluminescence with
a range of blue emission and quantum yield up to 80% in the solution. Extended
p conjugation molecules
of oligo-pPEs POSS maintain relatively high PL quantum efficiencies in the solid state, compared to
mono-pPEs POSS. A preliminary report is made of some of the materials as multilayer OLED components
with active dopants PVK and PBD.
Keywords:
p-Phenylene ethynylene
Oligomer
Ó 2010 Elsevier Ltd. All rights reserved.
Silsesquioxane
Photoluminescence
Light-emitting diode
1. Introduction
chromophores were incorporated into POSS framework, their pho-
toluminescence quantum efficiencies and thermal properties were
Polymeric and oligo(p-phenylene ethynylene)s (oligo-pPEs)
found to be significantly improved.21,24e26 The first introduction of
silsesquioxane materials to OLEDs was achieved in 2003, when Xiao
et al. reported the higher brightness and external quantum effi-
ciency of covalently anchored POSS at the chain-terminal of poly
(phenylene vinylene).21 However, during the past five years, con-
ventional reports of POSS in OLEDs have mainly explored the at-
tachment of fluorescence molecules to the corners of hyperbranched
POSS as a core. Octakis(dimethylsilyloxy)octasilsesquioxane is one
candidate, easily reacted with any alkenyl-fluorophores through the
hydrosilylation reaction to obtain full octa-functionalization. Our
laboratory firstly proposed a perfect octacarbazole functionalized-
POSS, which exhibited a strongly monomeric emission peak with
the suppression of excimers even in the solid state.22 Cho et al.
reported an electroluminescent POSS-based nanoparticle. POSS
cores were strongly confirmed to interrupt the aggregation of ter-
fluorene hyperbranches in the matrix.23 Froehlich et al. proposed the
same colour of emitters or a combination of different colours
hydrosilylated to POSS.24 However, these functionalities may show
some intramolecular quenching and energy transfer due to the high
flexibility of organic chain. Meanwhile, octa(vinyl)octasilsesquiox-
ane is one promising molecule readily cross-coupling through Heck
reaction with various haloaromatics. Extending conjugation on its
with rigid rod-like structures1,2 are one class of conjugated
p
-electron molecules that have in many applications, such as
sensors,3,4 solar cells,5,6 biological uses7,8 and electroluminescent
materials.9,10 Oligo-pPEs also show a unique photoluminescence as
monodisperse oligomers with precisely controlled repeating units,
when compared with polymeric system. Tuning the electronic
properties of oligomers can be done usually by controlling the
length of conjugation, directly substituted groups and structural
conformation.11e15 Nevertheless, there are a few examples to
functionalize terminal groups of oligomeric chain. Atienza et al.
first reported tuning electron transfer by a series of donor-bridge-
acceptor systems through oligo-pPE molecular wires.16
Recently, polyhedral oligomeric silsesquioxanes (POSS) with
rigid cage-like structures consisting of an inorganic SieOeSi core
and various organic substituents were found to be good candidates
for many applications in materials science.17e20 In organic light
emitting diodes (OLEDs), when photo- and electroactive p-electron
* Corresponding author. Tel.: þ66 2 201 5126; fax: þ66 2 354 7151; e-mail
address: scvuthichai@mahidol.ac.th (V. Ervithayasuporn).
0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.10.009

V. Ervithayasuporn et al. / Tetrahedron 66 (2010) 9348e9355
9349
rigid and reactive vinyl groups resulted in a change of electronic,
mophologies and amorphous properties, differed to small fluo-
rophore analogues. Sellinger et al. reported an 18% improvement in
external quantum efficiencies, when connected with a bromoar-
omatic hole transport material.25 By introducing pyrene groups, Lo
et al. obtained the highest external quantum and current efficiencies
of 2.63% and 8.28 cd/A, respectively.26 Another rigidly functional-
ized-POSS goes to octa(phenyl)octasilsesquioxane derivatives con-
taining highly functional groups on phenyl rings, such as amino,
bromo and iodo functions.27 For example, octa(bromophenyl)octa-
silsesquioxane was independently synthesized and reacted with the
Grignard reagent in order to conjugate with oligophenylenes.28,29
However, their functionalization has encountered some difficul-
ties, such as uncontrolled reaction numbers, separation and im-
precise structures. A few reports of designing POSS as a pendant into
conjugated molecules have been made. Miyake and Chujo recently
an approach of ‘click’ reaction. We further optimized the reaction
conditions by increasing the amount of catalyst, reaction time and
temperature. The complete reaction was finally observed in 5 days
under reflux. Column chromatography successfully separated a pure
form of 2-arm POSS monomer (3) in 80% yield.
To extend a p-phenylene ethynylene backbone for synthesizing
oligo-pPEs POSS (16, 17 and 18), co-monomers (10, 11 and 12) have
been prepared by using a ‘protected-alkyne route’ (Scheme 2a).
Firstly, ((4-iodophenyl)ethynyl)-trimethylsilane was cross-coupled
with commercially available ethynyl polycyclic aromatic derivatives:
2-ethynyl-6-methoxy-naphthalene (4), 9-ethynyl-phenanthrene (5)
and 1-ethynylpyrene (6) by Sonogashira cross-coupling reaction,
where led to the formation of protected precursors (7, 8 and 9, re-
spectively) in moderate yields. Subsequent treatment by meth-
anolysis reactionwith potassium carbonate cleaved the trimethylsilyl
(TMS) group from the TMS-linked alkyne to give a quantitative yield
of monomers (10, 11 and 12). These materials were available to use
without further purification for constructing the higher order-
structure of oligo-pPEs POSS.
reported that POSS wrapping along
p-conjugated polymers could
significantly enhance luminescence stabilities due to the steric effect
of the POSS units.30e32
Herein, we report the synthesis of new series of mono- and
oligo-pPEs POSS. Firstly, the novel 2-arm POSS (3) monomer was
prepared via ‘click’ chemistry and subsequent end-capping with
various polycyclic aromatics by Sonogashira cross-coupling re-
action to obtain pPE oligomers from deep blue to sky blue emission.
In consequence, all desirable products were purified and given in
an excellent yield with high thermal stability. These compounds
were also found to be promising candidates in OLEDs as dopant
materials.
For our approach to the synthesis of conjugated para-phenylene
ethynylene based on POSS, two families of ethynyl polycylclic ar-
omatics were readily used to grow oligomeric chain (Scheme 2b).
The introduction of palladium-catalyzed cross-coupling reaction
between a 2-arm POSS (3) and monomers (4, 5 and 6) provided the
new class of mono-pPEs POSS (13, 14 and 15) in excellent yield,
respectively. Similarly, the reactions between 3 and freshly pre-
pared materials (10, 11 and 12) gave a longer extended pPE back-
bone of oligo-pPEs POSS (16, 17 and 18), respectively.
2. Results and discussion
2.1. Synthesis
2.2. Thermal properties
The thermal stability of materials may be one criteria of the
lifetime and durability of electronic devices. High temperature and
oxygenated conditions usually decompose organic materials, pos-
sibly leading to a shorter lifetime of any device. Table 1 shows that
once mono- and oligo-pPEs possess the POSS as pendant groups,
their T5%loss were all above 330 ꢀC in air atmosphere. As well as, an
improving T5%loss of all materials was by 47 ꢀCe114 ꢀC, when
compared to purely organic parent molecules. This actually proves
that an inorganic silsesquioxane core could efficiently enhance the
thermal stability and prolong the lifetime of materials. The glass
transition temperature (Tg) is another important factor in de-
termining the stability of OLED devices and their shelf lifetimes.
The Tg values for these emitter functionalized-POSS materials are
all above 80 ꢀC as indicated in Table 1.
In order to evaluate the reaction condition, novel 2-arm POSS
monomer (2) (Scheme 1) was preliminarily synthesized via ‘click’
chemistry between freshly prepared mono azido-functionalized
POSS (1)33 and bis(propargyl)benzene. The 1,3-dipolar cycloaddition
reaction was carried out in the presence of Cuþ (reduced form of
CuSO4 in sodium ascorbate) as an active catalyst. Compound 1 was
completely consumed in 48 h at 40 ꢀC to form the 1,4-regioisomer of
2-arm POSS product 2 (94% yield). However, the similarly carried out
reaction between 1 and 1,4-diiodo-2,5-bis(prop-2-ynyloxy)benzene
was incomplete under the same reaction condition, evidenced by the
presence of remaining starting materials. This failure can be
explained by the steric effect on iodo-substituent benzene retarding
Scheme 1. Cuþ catalyzed double-click cycloaddition reactions: 2, CuSO4/sodium ascorbate/40 ꢀC-2 days, 94% yield; 3, CuSO4/sodium ascorbate/Cu powder/reflux-5 days, 80% yield.

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V. Ervithayasuporn et al. / Tetrahedron 66 (2010) 9348e9355
Scheme 2. Pd(0)-catalyzed Sonogashira cross-coupling reaction leading to: (a) polycyclic aromatic (p-phenylene ethynylene) monomers and (b) mono- and oligo-pPEs POSS.
2.3. Photophysical properties
The solution-state absorption and fluorescence spectra of
mono- and oligo-pPEs POSS were recorded in THF and are shown in
Fig. 1 and Table 2. By design, the band gap tuned from deep blue to
sky blue was achieved in both mono- and oligo-pPEs POSS, where
a red-shift of absorption and emission spectra was observed after
the aromatic number of end-capping molecules was increased. In
addition, the peak absorption and emission wavelengths of oligo-
pPEs POSS (16 and 17) were red-shifted compared to the corre-
sponding maxima for mono-pPEs POSS (13 and 14), respectively,
because of the extended conjugation in a main chain pPE. In-
terestingly, pyrene-linked molecules of 18 showed a blue-shift in
both the absorption and emission spectra compared to mono-pPEs
POSS (15).
Phenylene/ethynylene oligomers are typically fluorescent
(Vz0.6e0.8) and absorb strongly in the UV region.13,34 The ab-
sorption and emission bands shift to longer wavelengths upon
extension of the conjugation. However, longer oligomers possess
poor solubility and cause problems in the purification process.
Alternatively, it is possible to extend the absorption spectral
properties of these oligomers into the visible region via
p con-
jugation with aryl groups.35 In this study, the p-phenylene/
ethynylene oligomer was terminally capped with numbers of
polycyclic aromatics to extend and tune its photoresponsive na-
ture. The solubilities of the desired products in organic solvents
were also increased due to the presence of the grafted POSS
units.
The solid-state absorption and photoluminescence (PL) results
are also plotted in Fig. 1 and the data summarized in Table 2. The

V. Ervithayasuporn et al. / Tetrahedron 66 (2010) 9348e9355
9351
Fig. 1. Absorption spectra in THF solution (dash dot) and dropped cast film (dot) and emission spectra in THF solution (solid) and dropped cast film (dash) of materials: (a) 13, (b) 14,
(c) 15, (d) 16, (e) 17 and (f) 18.
a stronger
self-quenching.
pep interaction with neighbour molecules, which led to
Table 1
Thermal properties of parent molecules, mono- and oligo-pPEs POSS
Compounds
T5%loss (ꢀC)a
Tg (ꢀC)
2.4. Optical devices
7
8
9
13
14
15
16
17
18
255
282
311
332
348
358
369
363
366
EL devices named as dye-doped OLEDs were fabricated for the
emission characteristics of dopant 15 and 18. However, two types of
OLED structures were made to optimize device efficiency, designed
as devices A and B. While the OLED structure of device A for 15 was
composed of ITO/PEDOT:PSS/dopant(1e8% w/w):PBD:PVK/MPT/
LiF/Al, device B of 18 was ITO/PEDOT:PSS/PVK/dopant(3e12%
w/w):PBD:PVK/MPT/LiF/Al. The normalized EL spectra driven at
current density of 0.1 mA/cm2 with varied dopant concentrations
are shown in Fig. 2.
In Fig. 2, the EL spectra of 15 show the emission peak at 475 and
482 nm for dopant concentrations ꢁ5% and 8%, respectively. This
14 nm red shift between the diluted solution and doped OLED device
at low concentration (ꢁ5%) can be due to aggregation effects in the
solid. However, at high concentration (8%), the higher 21 nm red
shift, as well as the unusual luminescent pattern, indicated excimer
formation. Similarly, the EL spectra for 18 show the emission peak at
457 nm and a 14 nm red shift for every concentration (3e12%) of
doped material and no excimeric fluorescence was observed under
these concentrations (Fig. 2b). This evidence also confirms the solid
state properties of pure dopants (Table 2) in which, the extension of
80
182
107
135
197
173
a
TGA was performed at a heating rate of 10 ꢀC/min under air atmosphere.
Table 2
Maximum absorption, emission, and photoluminescence quantum yield of mono-
and oligo-pPEs POSS
Compounds
Solutiona
Solid state
Amax
Emmax
(nm)b
V
Amax
Emmax
(nm)b
V
(nm)
(nm)
13
14
15
16
17
18
373
390
420
385
388
403
409
421
461
428
432
443
0.81
0.81
0.87
0.82
0.86
0.84
388
389
461
426
399
410
480
470
484
476
533
503
0.09
0.17
0.11
0.28
0.31
0.37
p-conjugated backbone on oligo-pPEs POSS lowers the p interaction
a
Solvent¼THF (1ꢂ10ꢃ7 M).
between molecules as shown by a suppression of eximer.
b
Excitation wavelength¼350 nm; V, measurement done in excitation
OLED devices properties for 15 and 18 are also summarized in
Table 3. Devices having 15 as the dopant and the device A had
a turn-on voltage about 5.9e6.5 V with a low brightness (e2 cd/m2).
The maximum external quantum and luminous effiencies of 1.50%
and 4.54 cd/A, respectively, can be reached using 5% of dopant. Thus,
a forward light output of 100 cd/m2 was achieved at 8.0 V as well as
a current density at 2.34 mA/cm2. A different performance can be
seen for the device B doped with 18, where the turn-on voltage is
around 6.7e9.4 V. The highest doped concentration of 12% shows
the best device with the maximum quantum and luminous effi-
ciencies at 1.73 and 3.76, respectively. Thus, a bias voltage of 9.3 V
with a corresponding current density of 2.59 mA/cm2 is needed to
reach a forward light output of 100 cd/m2.
wavelength¼350 nm.
absorption and PL spectra of drop-cast films of 13e18 are red-
shifted, compared to the solution state. These spectroscopic fea-
tures display arising from interchain orbital interactions, generally
referred to as aggregation bands. Similarly, the quantum efficiency
of these aggregated systems is dramatically reduced in the solid
state. However, the extended
pPEs POSS (16, 17 and 18) maintain relatively high PL quantum
efficiencies when compared to mono-pPEs POSS (13, 14 and 15).
p conjugation molecules of oligo-
We suggest that without the elongated
polyaromatic at the chain-terminal mono-pPEs POSS possesses
p backbone of pPE, the

9352
V. Ervithayasuporn et al. / Tetrahedron 66 (2010) 9348e9355
Fig. 2. Normalized EL spectra operated at current density 0.1 mA/cm2 of dopants: (a) 15 and (b) 18.
Table 3
(DHBA) was dissolved in THF (10 mg/mL), and mixed with the
sample solution (0.5e1 mg/mL in THF) in 1:1 v/v ratio. The samples
were spotted onto the target and dried in air. Elemental analyses
were performed by CHNOS Elemental Analyzer, Vario EL III. Column
chromatography (CC): SiO2 60 (230e400 mesh, 40e63 mm) from
E. Merck. TLC glass plates coated with SiO2 60 F254 from E. Merck,
visualization by UV light.
UVevis absorption spectra of materials were collected by JASCO,
V-670 spectrometer. The PL and EL spectra and fluorescence quan-
tum yield were measured by C9920-02 Hamamatsu spectrometer.
The current density, voltage and external quantum efficiency of
OLED devices were determined by Keithley 4200 semiconductor
parameter analyzer system and an integrating sphere equipped
with a Si photodiode (S2281, Hamamatsu photonics). The luminous
efficiency was analyzed by a luminance metre (BM-9, Topcon).
OLED device properties of dopants: (a) 15 and (b) 18
ELmax
Current
density
(mA/cm2)c
Luminous
Efficiency
(cd/A)d
EQE
(%)e
(nm)
(a) % wt of 15
1%
3%
5%
8%
TVa
BVb
473
475
475
482
6.3
6.4
6.5
5.9
7.9
8.0
8.0
7.8
2.31
2.49
2.34
3.47
3.87
3.96
4.54
2.86
1.44
1.47
1.50
1.34
(b) % wt of 18
3%
5%
8%
456
457
457
457
7.9
7.8
9.4
6.7
11.1
9.7
10.8
9.3
8.34
4.03
4.30
2.59
1.15
2.51
2.26
3.76
1.45
1.66
1.39
1.73
12%
a
Turn-on voltage.
A bias voltage.
At 2 cd/m2.
b
c
4.2. Materials
d
e
At the light forward output of 100 cd/m2.
The external quantum efficiency.
1-Ethynylpyrene, 9-ethynyl-phenanthrene and 2-ethynyl-6-
methoxynapthalene were commercially available through Aldrich
and ((4-iodophenyl)ethynyl)trimethylsilane from Alfa Aesar
company. Materials for OLED devices, the host polymer as poly(9-
vinylcarbazole) (PVK) has a high molecular weight-average of
1,100,000 g/mol and electron-transporting molecule 2-(4-biphe-
nylyl)-5-phenyl-1,3,4,-oxadiazole (PBD) were purchased from
Aldrich. The high conductivity coating surface of poly(3,4-ethyl-
endioxythiophene)-poly(styrenesulfonate) formulation (PEDOT:PSS)
were purchased from Baytron P, Al 4083. All materials were used as
received without further purification.
3. Conclusions
We successfully demonstrated the synthesis and characteriza-
tion of new classes of mono- and oligo(p-phenylene ethynylene)s
end-capped with various polycyclic aromatics for tunable photo-
luminescence in the blue emission range and also grafting POSS as
a pendant group. We have shown that these materials derived from
cubic silsesquioxanes are very robust with high Tg>80 ꢀC and
exhibit excellent thermal stabilities to air (T5%loss>330 ꢀC). Thus,
their optical properties all showed high photoluminescence with
blue emission and quantum yield >80% in the solution. In the solid
state, we also found that the high order structure of extended
conjugation system on pPE backbone tends to suppress the
quenching process with a maintainable quantum yield. In OLED
applications, we make a preliminary report of some of the materials
as an active dopant in PVK and PBD matrix of multilayer OLEDs.
4.3. Synthesis
4.3.1. Synthesis of 1,4-di(triazole-POSS) benzene (2). Under
a
nitrogen atmosphere, 1,4-bis(prop-2-ynyloxy)benzene (0.162 g,
0.87 mmol) and 3 (1.72 g, 1.91 mmol) were dissolved in 12 mL of
THF. The flask was flushed with nitrogen, frozen and evacuated for
three times, after which CuSO4$5H2O (22 mg, 0.088 mmol) and
sodium ascorbate (51.7 mg, 0.261 mmol) in 0.30 mL of degassed
water were added. The reaction mixture was allowed to stir at 40 ꢀC
for 2 days. The solution was filtered through cotton and evaporation
of solvent giving a crude solid. The product was separated by col-
umn chromatography with elution in hexane:ethyl acetate (3:1)
(Rf¼0.25) to obtain a white solid (1.62 g, 0.818 mmol, 94% yield). 1H
4. Experimental
4.1. Instruments
1H (300 MHz), 1H (500 MHz), 13C (125 MHz), and 29Si (99 MHz)
NMR spectra were obtained in CDCl3 on a Varian spectrometer
model Unity INOVA. Chemical shifts are reported in parts per million
NMR (300 MHz, CDCl3):
d
¼7.57 (s, 2H), 6.94 (s, 4H), 5.16 (s, 4H), 4.37
(t, J¼7.5 Hz, 4H), 2.01 (quin, J¼7.8 Hz, 4H), 1.89 (m, 14H), 0.96 (d,
J¼6.6 Hz 84H), 0.66 (overlapped, 4H), 0.63 (m, 28H); 13C NMR
relative to CHCl3 (
d
7.26, 1H) and CDCl3 (
d
77.0, 13C). Matrix Assisted
(125 MHz, CDCl3): d 152.8, 144.3, 122.3, 115.7, 62.72, 52.57, 25.68,
Laser Desorption Ionization Time of Flight Mass Spectrometry
(MALDI-TOF MS) was performed using a Voyager-DE RP (Applied
Biosystems) in linear mode. The matrix 2,5-dihydroxybenzoic acid
25.66, 24.14, 23.87, 23.82, 22.43, 22.39, 9.24; 29Si NMR (99 MHz,
CDCl3, TMS):
d
ꢃ67.55, ꢃ67.84, ꢃ68.59 (relative intensity ratio
3:4:1); MALDI-TOF MS [C74H148N6O26Si16þNa]þ: calcd 2010.67,

V. Ervithayasuporn et al. / Tetrahedron 66 (2010) 9348e9355
9353
found 2010.11. Elemental analyses (C74H148N6O26Si16): calcd C
44.72, H 7.51, N 4.23; found C 44.65, H 7.63, N 4.21.
7.54 (m, 2H), 0.29 (s, 9H); 13C NMR (125 MHz, CDCl3):
d
132.0,
131.91, 131.44, 131.39, 131.22, 131.03, 129.6, 128.4, 128.3, 127.2, 126.3,
125.70, 125.65, 125.42, 124.53, 124.46, 124.28, 123.6, 122.9, 117.4,
104.7, 96.4, 94.8, 90.6, ꢃ0.062; MALDI-TOF MS [C29H22SiþH]þ:
calcd 399.16, found 399.2. Elemental analyses (C29H22Si): calcd C
87.39, H 5.56; found C 87.22, H 5.47.
4.3.2. Synthesis of 2,5-diiodo-1,4-di(triazole-POSS) benzene (3). Under
a nitrogen atmosphere, 1,4-diiodo-2,5-bis(prop-2-ynyloxy)benzene
(0.6425 g, 1.70 mmol) and 3 (3.30 g, 3.664 mmol) were dissolved in
30 mL of THF. The reaction flask was flushed with nitrogen, frozen
and evacuated three times, after which CuSO4$5H2O (160 mg,
0.64 mmol) and sodium ascorbate (380 mg,1.92 mmol) in 0.50 mL of
degassed water and Cu powder (0.10 g) were added. The solution
mixture was refluxed for 5 days. The solution was filtered through
cotton and the solvent evaporated to give a crude solid. The crude
product was dissolved in a small amount of dichloromethane and
separated by column chromatography with elution in hexane/ethyl
acetate (4:1) (Rf¼0.60) to obtain white solid product (3.04 g,
4.5. General procedure for the deprotection of polycylic
aromatic derivatives (10, 11 and 12)
Compounds (7, 8 or 9) (0.20 g) were dissolved in THF (15 mL),
followed by methanol (5 mL). The flask was flushed with nitrogen
after which K2CO3 (0.020 g) as a catalytic methanolysis was added
and kept stirring for an hour. Evaporation of solvent gave the crude
of deprotected products, further washed with dionized water, filter
and dried. The products (10, 11, or 12) were used through next step
without further purification.
1.36 mmol, 80% yield). 1H NMR (300 MHz, CDCl3):
d 7.67 (s, 2H), 7.38
(s, 2H), 5.20 (s, 4H), 4.39 (t, J¼7.2 Hz, 4H), 2.08 (quin, J¼7.5 Hz, 4H),
1.91 (m,14H), 0.96 (d, J¼6.6 Hz, 84H), 0.67 (overlapped, 4H), 0.62 (m,
28H); 13C NMR (125 MHz, CDCl3):
d
152.7, 143.5, 123.7, 122.6, 86.58,
4.6. General procedure for the synthesis of mono- and oligo
(p-phenylene ethynylene)s end-capping with polycyclic
aromatics (13e18)
64.72, 52.67, 25.69, 24.25, 23.87, 23.82, 22.44, 22.41, 9.25; 29Si NMR
(99 MHz, CDCl3, TMS):
d
ꢃ67.52, ꢃ67.84, ꢃ68.59 (relative intensity
ratio 3:4:1); MALDI-TOF MS [C74H146I2N6O26Si16þNa]þ: calcd
2261.46, found 2261.69. Elemental analyses (C74H146I2N6O26Si16):
calcd C 39.69, H 6.57, N 3.75; found C 39.64, H 6.72, N 3.75.
2-Arm POSS monomer (3) (0.20 g, 0.0894 mmol) and polycyclic
derivatives (4, 5, 6, 10, 11, or 12) (0.210 mmol) were dissolved in THF
(6 mL) and piperidine (0.6 mL) in an oven-dried Schlenk flask. The
flask was flushed with nitrogen after which (Ph3P)2PdCl2 (3.2 mg,
0.00459 mmol) and CuI (1.8 mg, 0.00918 mmol) were added. The
mixture was allowed to stir at room temperature overnight, after
which the solvent was removed. The crude mixture was dissolved
in dichloromethane and washed with 0.5 M HCl and water. The
organic layer was dried over Na2SO4 and the solvent was removed.
The resulting product was purified by column chromatography.
4.4. General procedure for the synthesis of polycyclic
aromatic derivatives (7, 8 and 9)
(4-(Iodophenyl)ethynyl)trimethylsilane (0.30 g, 0.999 mmol)
and ethynyl polycyclic aromatic derivatives (4, 5, or 6) (1.20 mmol)
were dissolved in tetrahydrofuran (13 mL) and piperidine (1 mL) in
an oven-dried Schlenk flask. The flask was flushed with nitrogen
after which (Ph3P)2PdCl2 (0.035 g, 0.05 mmol) and CuI (0.0095 g,
0.05 mol) were added. The mixture was allowed to stir at room
temperature for overnight. The solvent was removed and the
mixture was dissolved in dichloromethane and further washed
with 0.5 M HCl and water. The organic layer was dried over Na2SO4
and evaporation of solvent gave a crude. The resulting products
were purified by column chromatography and recrystallization.
4.6.1. Compound 13. Purification by flash chromatography on silica
gel with gradient eluent (CH2Cl2 and CH2Cl2/ethylacetate 100:1)
Rf¼0.45 provided a light yellow solid (197 mg, 0.0840 mmol, 94%
yield). 1H NMR (300 MHz, CDCl3):
d 7.98 (s, 2H), 7.73e7.69 (m, 4H),
7.66 (s, 2H), 7.55 (m, 2H), 7.23 (s, 2H), 7.19e7.16 (m, 2H), 7.13 (m,
2H), 5.36 (s, 4H), 4.33 (t, J¼7.2 Hz, 4H), 3.94 (s, 6H), 2.02 (pent,
J¼7.8 Hz, 4H), 1.88e1.75 (m, 14H), 0.96e0.91 (m, 84H), 0.64 (over-
lapped, 4H), 0.59 (d, J¼7.2 Hz, 28H); 13C NMR (125 MHz, CDCl3):
4.4.1. Compound 7. Purification by flash chromatography on silica
gel (hexane/CH2Cl2 1:1) Rf¼0.74 and further recrystallization in
acetone; 255 mg (72% yield) as a colourless crystal. 1H NMR
d
158.4, 153.4, 144.3, 134.2, 131.4, 129.4, 128.9, 128.5, 126.8, 122.4,
119.5, 118.3, 118.0, 114.8, 105.8, 96.1, 85.2, 64.4, 55.3, 52.6, 25.7, 25.6,
24.2, 23.84, 23.80, 22.42, 22.36, 9.28; MALDI-TOF MS
[C100H164N6O28Si16þNa]þ: calcd 2368.78, found 2369.14. Elemental
analyses (C100H164N6O28Si16): calcd C 51.16, H 7.04, N 3.58; found C
51.45, H 7.34, N 3.77.
(500 MHz, CDCl3):
1H), 7.49 (m, 4H), 7.18 (m,1H), 7.12 (s,1H), 3.93 (s, 3H), 0.262 (s, 9H);
13C NMR (125 MHz, CDCl3):
158.4, 134.2, 131.89, 131.48, 131.36,
d
7.97 (s, 1H), 7.69e7.60 (t, J¼7.5 Hz, 2H), 7.54 (m,
d
131.31, 131.28, 129.46, 129.28, 128.93, 128.85, 128.45, 126.95, 126.77,
125.52, 122.69, 119.47, 117.82, 105.78, 104.68, 96.95, 91.95, 88.73,
55.37, 55.33, ꢃ0.074, ꢃ0.101; MALDI-TOF MS [C24H22OSiþH]þ: calcd
355.15, found 355.1. Elemental analyses (C24H22OSi): calcd C 81.31, H
6.25; found C 81.25, H 6.46.
4.6.2. Compound 14. Purification by flash chromatography on silica
gel with gradient solvent (CH2Cl2 and CH2Cl2/ethylacetate 100:1)
Rf¼0.65 provided a yellow solid (0.186 g, 0.0780 mmol, 87% yield).
1H NMR (300 MHz, CDCl3):
d
8.72 (t, J¼9.0 Hz, 4H), 8.58 (d, J¼8.1 Hz,
4.4.2. Compound 8. Purification by recrystallization in acetone;
2H), 8.12 (s, 2H) 7.91 (m, 2H), 7.70e7.62 (m, 6H), 7.67 (overlapped,
2H), 7.54 (t, J¼7.8 Hz, 2H), 7.39 (s, 2H), 5.45 (s, 4H), 4.26 (t, J¼7.2 Hz,
4H), 1.95 (m, 4H), 1.88 (m, 14H), 0.96 (m, 84H), 0.60 (m, 28H), 0.54
285 mg (76% yield) as light yellow solid. 1H NMR (500 MHz, CDCl3):
d
8.72 (m, 1H), 8.68 (d, J¼8.0 Hz, 1H), 8.53 (m, 1H), 8.09 (s, 1H), 7.89
(d, J¼7.5, 1H), 7.73e7.67 (m, 3H), 7.63 (m, 1H), 7.62 (m, 2H), 7.52 (m,
2H), 0.28 (s, 9H); 13C NMR (125 MHz, CDCl3):
132.1, 131.9, 131.5,
(overlapped, 4H); 13C NMR (125 MHz, CDCl3):
d 153.7, 143.9, 131.8,
d
131.2, 131.0, 130.4, 130.1, 128.7, 127.6, 127.2, 127.1, 127.02, 127.03,
122.8, 122.7, 122.6, 119.6, 117.2, 114.6, 94.2, 90.2, 64.0, 52.6, 25.7,
25.6, 24.1, 23.83, 23.80, 22.4, 22.3, 9.27; MALDI-TOF MS
[C106H164N6O26Si16þNa]þ: calcd 2408.79, found 2409.00. Elemental
analyses (C106H164N6O26Si16): calcd C 53.32, H 6.92, N 3.52; found C
53.11, H 7.05, N 3.72.
131.2, 130.9, 130.4, 130.1, 128.6, 127.59, 127.14, 127.12, 127.00, 126.9,
123.4, 123.1, 122.8, 122.6, 119.4, 104.6, 96.4, 93.5, 89.7, ꢃ0.074;
MALDI-TOF MS [C27H22SiþH]þ: calcd 375.16, found 375.2. Elemen-
tal analyses (C27H22Si): calcd C 86.58, H 5.92; found C 86.44, H 5.68.
4.4.3. Compound 9. Purification by flash chromatography on silica
gel (hexane/CH2Cl2 10:1) Rf¼0.35 and further recrystallization in
acetone; 276 mg (69% yield) as yellow solid. 1H NMR (500 MHz,
4.6.3. Compound 15. Purification by flash chromatography on silica
gel with gradient eluent (CH2Cl2 and CH2Cl2/ethylacetate 100:1)
Rf¼0.70 provided a yellow solid (182 mg, 0.0748 mmol, 84% yield).
CDCl3):
d
8.65 (d, J¼9.5 Hz, 1H), 8.24e8.02 (m, 8H), 7.66 (m, 2H),

9354
V. Ervithayasuporn et al. / Tetrahedron 66 (2010) 9348e9355
1H NMR (300 MHz, CDCl3):
d
8.70 (d, J¼9.0 Hz, 2H), 8.25e8.03 (m,
substrates were treated by UV ozone for 30 min. PEDOT:PSS solu-
tion was spin-coated onto the ITO surface with a typical spinning
speed and time at 1600 rpm and 30 s, respectively. The film coat
was then dried over the hot plate 120 ꢀC for 10 min, giving 60 nm of
thickness. PVK and PBD in a weight ratio of 3:2, followed by addi-
tional concentration of dopant emitters (15) at 1%, 3%, 5% and 8% of
total weight, were dissolved in chlorobenzene solution with total
solid concentration of 15 mg/mL. The mixture solution was then
spin-coated onto the PEDOT:PSS surface with 1600 rpm for 30 s
giving 60 nm of thickness, followed by heating at 70 ꢀC for 10 min in
a nitrogen-filled glove box and then immediately transferred into
a vacuum for deposition. 2,4-Bis-biphenyl-4-yl-6-(40-pyridin-2-yl-
biphenyl-4-yl)-[1,3,5]triazine (MPT) (30 nm), LiF (0.5 nm) and Al
(100 nm) cathode were deposited layer by layer on top of a spin-
coating device by the thermal evaporation, respectively.
16H), 7.73 (s, 2H), 7.44 (s, 2H), 5.50 (s, 4H), 4.24 (t, J¼7.5 Hz, 4H),1.97
(m, 4H), 1.85 (m, 14H), 0.95 (m, 84H), 0.59 (m, 28H), 0.50 (over-
lapped, 2H); 13C NMR (125 MHz, CDCl3):
d 153.6, 144.0, 132.1, 131.4,
131.3,131.1,129.4,128.3,127.3,126.3,125.8,125.6,124.6,124.5,124.3,
122.8, 117.7, 117.2, 114.8, 95.2, 91.5, 64.1, 52.6, 25.7, 25.6, 24.0, 23.8,
22.4, 22.3, 9.21; MALDI-TOF MS [C110H164N6O26Si16þNa]þ: calcd
2455.79 found 2456.53. Elemental analyses (C110H164N6O26Si16):
calcd C 54.24, H 6.79, N 3.45; found C 54.38, H 6.55, N 3.49.
4.6.4. Compound 16. Purification by flash chromatography on silica
gel with gradient eluent (CH2Cl2 and CH2Cl2/ethylacetate 100:1)
Rf¼0.55 provided light yellow crystals (212 mg, 0.0832 mmol, 93%
yield). 1H NMR (300 MHz, CDCl3):
d 7.99 (s, 2H), 7.74e7.70 (m, 4H),
7.63 (s, 2H), 7.56e7.50 (m, 2H), 7.53e7.52 (overlapped, 8H), 7.21 (s,
2H), 7.19e7.16 (m, 2H), 7.13 (m, 2H), 5.33 (s, 4H), 4.37 (t, J¼7.2 Hz,
4H), 3.94 (s, 6H), 2.05 (pent, J¼8.1 Hz, 4H), 1.87 (m, 14H), 0.96 (m,
84H), 0.67 (overlapped, 4H), 0.61 (m, 28H); 13C NMR (125 MHz,
4.7.2. Device B. The multilayer OLED with ITO/PEDOT:PSS/PVK/
PVK:PBD:Dopant/MPT/LiF/Al structure was fabricated. The sub-
strate ITO was cleaned following as an identical treatment of de-
vice (A). PEDOT:PSS solution was spin-coated onto the ITO surface
with a typical thickness 60 nm and then dried over the hot plate
120 ꢀC for 10 min. Pure PVK in chlorobenzene solution (10 mg/mL)
was spin-coated on top of PEDOT:PSS to obtain a 50 nm of thick-
ness and quickly moved to nitrogen-filled glove box for drying at
70 ꢀC for 10 min. PVK and PBD in a weight ratio of 3:2, followed by
additional concentration of dopant emitters (18) at 3%, 5%, 8% and
12% of total weight, were dissolved in chlorobenzene solution
with total solid concentration of 15 mg/mL. The mixture solution
was then spin-coated onto the PVK surface with 1600 rpm for 30 s
giving about 60 nm of thickness, followed by heating at 70 ꢀC for
10 min in a nitrogen-filled glove box and then immediately
transferred into a vacuum for deposition. MPT (30 nm), LiF
(0.5 nm) and Al (100 nm) cathode were deposited layer by layer on
CDCl3): d 158.4,153.4,144.1,134.2,131.6,131.49,131.41,131.39,128.9,
128.5, 126.9, 123.6, 122.73, 122.42, 119.5, 118.2, 117.8, 114.7, 105.8,
95.3, 92.2, 88.8, 87.3, 64.2, 55.4, 52.6, 25.7, 25.6, 24.2, 23.9, 23.8,
22.42 22.37, 9.28; MALDI-TOF MS [C116H172N6O28Si16þNa]þ: calcd
2569.85, found 2570.56. Elemental analyses (C116H172N6O28Si16):
calcd C 54.68, H 6.80, N 3.30; found C 54.55, H 6.78, N 3.32.
4.6.5. Compound 17. Purification by flash chromatography on sil-
ica gel with gradient eluent (CH2Cl2 and CH2Cl2/ethylacetate
100:1) Rf¼0.70 provided a yellow solid (0.220 mg, 0.0851 mmol,
95% yield). 1H NMR (500 MHz, CDCl3):
d 8.74 (m, 2H), 8.69 (d,
J¼8.0 Hz, 2H), 8.55 (m, 2H), 8.11 (s, 2H), 7.90 (d, J¼7.0 Hz, 2H),
7.74e7.61 (m, 8H), 7.674e7.659 (d (overlapped), J¼7.5 Hz, 4H),
7.648 (s (overlapped), 2H), 7.58e7.57 (d, J¼8.5 Hz, 4H), 7.24 (s, 2H),
5.36 (s, 4H), 4.38 (t, J¼7.5 Hz, 4H), 2.04 (pent, J¼7.5 Hz, 4H) 1.87
(oct; J¼6.0 Hz, 14H), 0.95 (m, 84H), 0.66 (overlapped, 4H), 0.61 (t,
top of
a spin-coating device by the thermal evaporation,
J¼6.0 Hz, 28H); 13C NMR (125 MHz, CDCl3):
d
153.4, 144.1, 132.2,
respectively.
132.0, 131.74, 131.69, 131.59, 131.54, 131.2, 130.9, 130.4, 130.1, 128.7,
128.5, 127.7, 127.3, 127.1, 127.0, 123.4, 123.1, 122.8, 122.5, 122.3,
119.4, 118.3, 114.7, 95.3, 93.6, 89.8, 87.5, 64.2, 52.6, 26.1, 25.7, 25.6,
25.1, 24.2, 23.91, 23.85, 23.82, 23.76, 22.42, 22.38, 9.28; MALDI-TOF
MS [C122H172N6O26Si16þNa]þ: calcd 2609.86, found 2610.63. Ele-
mental analyses (C122H172N6O26Si16): calcd C 56.62, H 6.70, N 3.25;
found C 56.91, H 6.58, N 3.11.
Acknowledgements
V.E. and X.W. thank to Ministry of Education, Culture, Sports,
Science, and Technology (MEXT), Japanese Government for sup-
porting a scholarship at JAIST.
Supplementary data
4.6.6. Compound 18. Purification by flash chromatography on silica
gel with gradient eluent (CH2Cl2 and CH2Cl2/ethylacetate 100:1)
Rf¼0.75 provided a yellow solid product (235 mg, 0.0892 mmol, 99%
Supplementary data available for 1H NMR spectra and TGA
profiles of materials. Supplementary data related to this article can
be found online at doi:10.1016/j.tet.2010.10.009. These data include
MOL files and InChiKeys of the most important compounds
described in this article.
yield).1H NMR (300 MHz, CDCl3):
d
8.68 (d, J¼9.3 Hz, 2H), 8.24e8.05
(m, 16H), 7.72 (d, J¼8.7 Hz, 4H), 7.669 (s, 2H), 7.61 (d, J¼8.4 Hz, 4H),
7.25 (s, 2H), 5.37 (s, 4H), 4.37 (t, J¼7.2 Hz, 4H), 2.07 (pent, J¼7.5 Hz,
4H), 1.84 (m, 14H), 0.95 (d, J¼6.0 Hz, 84H), 0.68 (overlapped, 4H),
0.62 (m, 28H); 13C NMR (125 MHz, CDCl3):
d 153.3,144.1,131.9,131.7,
References and notes
131.6,131.5,131.2,131.0,129.6,128.4,128.3,127.2,126.3,125.7,125.4,
124.6, 124.5, 124.3, 123.6, 123.0, 122.5, 118.3, 117.4, 114.7, 95.4, 94.8,
90.8, 87.5, 64.2, 52.7, 25.6, 24.2, 23.9, 23.8, 22.4, 22.3, 9.30; MALDI-
TOF MS [C126H172N6O26Si16þNa]þ: calcd 2657.86, found 2657.59.
Elemental analyses (C126H172N6O26Si16): calcd C 57.41, H 6.58, N
3.19; found C 57.37, H 6.44, N 3.39.
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